1. Technical Field
The disclosure relates to an engine combustion system having two turbines in the engine exhaust.
2. Background Art
Internal combustion engines have a cylinder block and a cylinder head to form the individual cylinders, that is to say, combustion chambers. Pistons reciprocate within cylinder liners in the cylinder block.
The cylinder head contains actuatable valves for controlling flow into and out of the combustion chambers with the valve drivetrain conventionally located in the cylinder head.
Intake ducts leading to intake valves and exhaust ducts leading away from exhaust valves are at least partially integrated into the cylinder head. For example, exhaust ducts of at least two cylinders may converge into an overall exhaust duct within the cylinder head. The convergence of the many exhaust ducts into an overall duct may be called an exhaust manifold.
Downstream of the exhaust manifold, a turbine of a turbocharger may be situated. Furthermore, an exhaust gas aftertreatment system may be included in the engine exhaust as well.
It is desirable to arrange the turbine of the turbocharger as close to the exhaust valves as possible to optimally utilize the exhaust-gas enthalpy, i.e., prior to cool down. Such an arrangement aids in providing a fast response behavior of the turbocharger and to provide a short path to exhaust gas aftertreatment devices to facilitate quick light-off of the aftertreatment device following a cold start of the engine.
Thermal inertia of the part of the exhaust ducts situated between the exhaust valve and the exhaust aftertreatment system, or between the exhaust valve and the turbine, should therefore also be as low as possible, which can be obtained by reducing the mass and the length of the corresponding parts.
To facilitate low thermal inertia, it is expedient for the exhaust ducts to converge within the cylinder head so as to form an integrated exhaust manifold. The length of the exhaust ducts is reduced as a result of the integration. This improves the response behavior of the turbine and the enthalpy of the exhaust gases at the inlet into the turbine is increased.
Turbocharged internal combustion engines are however often equipped with a plurality of exhaust-gas turbochargers to improve the torque characteristics of the internal combustion engine over a wide operating range. While a single turbine may be close-coupled, that is to say positioned close to the cylinder head, as a result of the integration of the manifold, a dual-turbocharger arrangement that is close-coupled is desired.